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How to exactly test a transformer?

The transformer plays an important part in many electrical applications. It is a device that is used to transfer electrical energy from one circuit to another. In Alternating Current (AC) the transformer will either increase or decrease the voltage as it makes the transfer. The two types of AC transformers available in the market are - linear transformer and switch mode power transformer which are different in design. The linear transformer is used in radios, project kits and VCD's. The switch mode transformers are used in monitors, TV's and fax etc.

The direct current voltage cannot be changed by a transformer. The main work of a transformer is to change the AC voltage. The transformer is made of two or more coils which are wound round the same core. In power transformers, the core is generally made of iron. In radio frequency transformers the core is generally made of ferrite of air.

A step down transformer has lower AC voltage output in its secondary windings compared to the AC input voltage in the primary windings. A step up transformer has higher secondary windings compared to the AC input voltage in the primary windings. The transformer is coated with shellac, enamel or varnish which helps in insulating adjacent turns from shorts between windings.

These transformers have to be tested when they fail to work. This testing should be carried out by people who are well informed about the way the transformers work and know how to repair it. Generally, in electronic equipments the failure of a transformer is rare. If a lot of current passes through the coil or windings and it heats up, then it can either open up completely or the insulation between the turns of the wires can be affected resulting in the coil being partially or completely shorted.

The continuity of the primary and secondary windings can be checked and you will know when it is open. When checking the linear transformer, you can apply the AC voltage to the primary winding and see the result in the secondary winding. If there is no or low voltage then it means that the windings are open or shorted. You can also check if there is overheating and there are any areas that are burnt or blackened.

The best method to test a transformer would be to remove the transformer from the board. Then you should first check the primary windings which are generally the ones to be at fault. To find out the primary winding, you should see the filter cap the positive pin to see where it goes in the circuit. This will lead you to the pin of the transformer. You should then check the middle pin which is the Drain. This will lead you to another pin of the transformer. These two pins make the primary windings. By checking the resistance you will find out if it is open. To check whether it is shorted, you have to use the ringer test. If it is shorted, it will blow up the power section.

The ringer tester that is the cheapest is the flyback tester or the Dick Smith Lopt Meter. When the probes are connected to the primary windings, the result is seen on the Led bar graph. The indications on the bar will show you the condition of the windings. If the bar shows 4-8, it means that the winding is in good condition. If the bar shows 1-2, it means that thee is partial short, if the Led goes off completely, it means that there is big short.

An expensive type of ringer tester will check and test the capacitor and all the windings. It will be able to check and test low voltage transformers,high voltage transformers,current transformers, pulse transformers,electric transformers and custom transformers.

Another method of testing is to use a light bulb. You should remove one of the primary windings pin. Then you should connect it to a 60 watt bulb. One end will be connected to the circuit and the other end will be connected to the transformer pin. If the light in the bulb shines, it means that the winding is shorted. If the light in the bulb goes off it means that the winding is alright.

It is necessary to have expertise and know the work well before testing a transformer. If you do not know anything about it, you should be aware of the different methods of testing, so that you will know how the person testing the transformer is performing his job and you will be well informed about its various aspects.